How do bacteria cows to get nutrients from grass?

The digestive system contains various enzymes that can help in the proper digestion of food, and we all know that digestive system starts from the mouth. But the human digestion is different than that of the cow. Cows have slight difficulty to digest food than humans because of cellulose found in hay and grass. Good thing that there are billions of bacteria and organisms that live and die in the rumen (biggest of the four stomachs) of the cow. These organisms they break down food and efficiently convert them to nutrient the cow needs in order to prevent starvation.